Strength and water absorption for gypsum—cement—silica fume blends of improved performance

Abstract

The present work describes results of testing gypsum—cement—silica fume blends having gypsum binder contents of 65, 75 and 85% at various silica fume/Portland cement ratios: 1/4, 2/3, 3/2 and 4/1. Cases of extra expansion and cracking due to ettringite formation were not revealed. It is shown that the hydraulic properties are developed in time in a diflerent manner for various compositions. Some of the blends achieved a high wet/dry strength ratio exceeding 0·6 after 200 days of water curing. This is explained by the development of a microstructure in which gypsum crystals were engulled by C-S-H. The optimum compositions were revealed by high absolute values of compressive strength in the water-saturated state, as well as low values of water absorption. The high values of water absorption for some compositions together with the low values of strength in the wet state are due to the extra content of silica fume, which is not needed for pozzolanic reaction and can be freely removed from the structure by washing.